1. Field of the Invention
The present invention relates to a lens barrel including a cam ring for moving lens groups in an optical axis direction.
2. Description of the Related Art
In a conventional lens barrel known in the art, in which each of linearly guided front and rear lens group frames is provided with a plurality of follower pins which are respectively engaged in a corresponding cam grooves formed on a rotating cam ring so that the linearly guided front and rear lens group frames move in an optical axis direction without rotating about the optical axis by rotation of the cam ring to move each of the front and rear lens group frames between an accommodation position and a photographing position in front of the accommodation.
However, if the angle of inclination of each cam groove relative to a circumferential direction of the cam ring (i.e., the pitch of each cam groove) is reduced to achieve a smooth movement of each lens group frame and if the length of each cam groove is increased to increase the maximum angle of rotation of the cam ring, the cam grooves for the first lens group frame and the cam grooves for the second lens group frame may interfere with each other.
The present invention provides an improved lens barrel wherein a large angle of rotation of a cam ring thereof can be secured even if cam grooves formed on the cam ring are shortened.
For example, a lens barrel includes an optical system including a front lens group and a rear lens group; a front lens frame which supports the front lens group, the front lens frame including a first cam follower and being guided linearly in an optical axis direction without rotating about the optical axis; a rear lens frame which supports the rear lens group and includes a second cam follower; and a cam ring which is driven to rotate about the optical axis and includes a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove of the cam ring includes a front-lens-group accommodation portion which accommodates the first cam follower, and a rear-lens-group-accommodation portion which accommodates the second cam follower and is positioned closer to the front side of the cam ring than the front-lens-group accommodation portion, the front lens group and the rear lens group being positioned in respective accommodation positions thereof when the first cam follower and the second cam follower are engaged in the front-lens-group accommodation portion and the rear-lens-group-accommodation portion, respectively. One of the front lens frame and the rear lens frame includes a linear guide groove which extends parallel to the optical axis and a wide-width engaging portion which communicatively connects to a front end of the linear guide groove, the wide-width engaging portion having a greater width than the linear guide groove in a circumferential direction of the one of the front lens frame and the rear lens frame. The other of the front lens frame and the rear lens frame includes a linear guide projection which is selectively engaged in one of the linear guide groove and the wide-width engaging portion. The cam groove of the cam ring further includes a straight connecting portion formed so as to extend between the front-lens-group accommodation portion and the rear-lens-group-accommodation portion to extend linearly in a direction inclined with respect to both the optical axis and a circumferential direction of the cam ring, a width of the straight connecting portion being substantially the same as a diameter of the second cam follower. The rear-lens-group-accommodation portion is formed as a dead end of the cam groove which only allows the second cam follower to move toward the straight connecting portion therefrom. The linear guide projection is engaged in the wide-width engaging portion to thereby allow the rear lens frame to rotate with respect to the front lens frame when the front lens group and the rear lens group are positioned in the respective accommodation positions. If the cam ring rotates when the front lens group and the rear lens group are positioned in the respective accommodation positions, the second cam follower is rotated together with the cam ring, the second cam follower being positioned in one of the rear-lens-group-accommodation portion and the straight connecting portion in the vicinity of the rear-lens-group-accommodation portion when the linear guide projection reaches the front end of the linear guide groove from the wide-width engaging portion to be thereby prevented from rotating with respect to the front lens frame. The second cam follower is moved on a side edge of the straight connecting portion toward the front-lens-group accommodation portion so that the linear guide projection enters the linear guide groove to be properly engaged therein after the linear guide projection reaches the front end of the linear guide groove from the wide-width engaging portion.
It is desirable for the cam groove to include a moving section which is connected to one end portion of the front-lens-group accommodation portion on the side opposite from the straight connecting portion, the moving section being inclined in an opposite direction to the inclination direction of the straight connecting portion. When the second cam follower is moved rearward in the straight connecting portion so that the linear guide projection enters the linear guide groove, the first cam follower is moved forward in the moving section to move the front lens frame forward in the optical axis direction.
It is desirable for the cam groove to include a moving section for moving the first cam follower and the second cam follower to move the front lens frame and the rear lens frame in the optical axis direction, the moving section being connected to one end portion of the front-lens-group accommodation portion on the side opposite from the straight connecting portion. The moving section is curved to extend firstly rearward and subsequently forward, from the front-lens-group accommodation portion. The front lens frame presses the rear lens frame rearward to move the second cam follower from the rear-lens-group-accommodation portion to the straight connecting portion when the first cam follower moves rearward from the front-lens-group accommodation portion to the moving section by rotation of the cam ring. When the first cam follower subsequently moves forward in the moving section, the front lens frame presses the rear lens frame forward to move the second cam follower in the straight connecting portion back toward the rear-lens-group-accommodation portion, the linear guide projection reaching the front end of the linear guide groove from the wide-width engaging portion before the second cam follower reaches the rear-lens-group-accommodation portion.
It is desirable for the second follower pin to stay in the rear-lens-group-accommodation portion and rotate together with the cam ring without moving relative to the rear-lens-group-accommodation portion during the time the first cam follower moves from the front-lens-group accommodation portion to the moving section.
It is desirable for the wide-width engaging portion and the linear guide groove to be formed on an inner peripheral surface of the front lens frame. The linear guide projection is formed on an outer peripheral surface of the rear lens frame. A rear side edge of the wide-width engaging portion presses the linear guide projection forward when the first cam follower moves forward in the moving section.
The lens barrel can be a zoom lens barrel and the moving section can constitute a zooming section for moving the front lens group and the rear lens group to perform a zooming operation.
It is desirable for the front-lens-group accommodation portion to be shaped to allow the first cam follower to move in the optical axis direction in the front-lens-group accommodation portion by a predetermined amount of movement.
It is desirable for the front lens frame to include an inner flange for supporting the front lens group, a circumferential opening being formed on the inner flange. The rear lens frame can include a front projecting portion, on which the linear guide projection is formed, the front projecting portion projecting forward to extend through the inner flange through the circumferential opening when the rear lens frame is positioned in the vicinity of the accommodation position thereof.
According to another embodiment, a lens barrel is provided including an optical system including a front lens group and a rear lens group; a front lens frame which supports the front lens group, the front lens frame including a first cam follower and being guided linearly in an optical axis direction without rotating about the optical axis; a rear lens frame which supports the rear lens group and includes a second cam follower; and a cam ring which is driven to rotate about the optical axis and includes a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove of the cam ring includes a front-lens-group accommodation portion which accommodates the first cam follower, and a rear-lens-group-accommodation portion which accommodates the second cam follower, the front lens group and the rear lens group being positioned in respective accommodation positions thereof when the first cam follower and the second cam follower are engaged in the front-lens-group accommodation portion and the rear-lens-group-accommodation portion, respectively. The cam groove further includes a straight connecting portion formed so as to extend between the front-lens-group accommodation portion and the rear-lens-group-accommodation portion to extend linearly in a direction inclined with respect to both the optical axis and a circumferential direction of the cam ring, a width of the straight connecting portion being substantially the same as a diameter of the second cam follower. The rear-lens-group-accommodation portion is formed as a dead end of the cam groove which only allows the second cam follower to move toward the straight connecting portion therefrom. One of the front lens frame and the rear lens frame includes a linear guide groove which extends parallel to the optical axis and a wide-width engaging portion which communicatively connects to a front end of the linear guide groove, the wide-width engaging portion having a greater width than the linear guide groove in a circumferential direction of the front lens frame and the rear lens frame. The other of the front lens frame and the rear lens frame includes a linear guide projection which is selectively engaged in one of the linear guide groove and the wide-width engaging portion. The second cam follower is positioned in the rear-lens-group-accommodation portion when the rear lens frame is positioned at one end of a rotational range thereof which is determined by an engagement of the linear guide projection with the wide-width engaging portion. The second cam follower is positioned in one of the rear-lens-group-accommodation portion and the straight connecting portion in the vicinity of the rear-lens-group-accommodation portion when the rear lens frame is positioned at the other end of the rotational range thereof.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-335563 (filed on Oct. 31, 2001) which is expressly incorporated herein by reference in its entirety.